We present an energy roadmap for the US light duty vehicle (LDV) sector that efficiently utilizes natural gas (NG) and transitions to renewable energy and carbon sources as they become economical. We use well-to-wheels (WTW) efficiency to compare alternative NG transportation pathways. If internal combustion engine vehicles (ICEVs) remain prevalent, then compressed natural gas (CNG) is the favored fuel. Among electric powertrains, centralized electricity generation with battery electric vehicle (BEV) is more efficient than on-board generation with fuel-cell vehicles (FCV). Plug-in hybrid electric vehicles (PHEVs) balance driving range against WTW efficiency, and provide flexibility in sourcing electricity from different energy sources. Despite these efficient WTW pathways, supplying NG for the LDV sector is estimated to decrease the lifetime of current US NG reserves to about 60 years. Beyond this period, compressed methane derived from biomass can replace CNG, and utilize the would-be developed CNG infrastructure. The LDV biomass requirement depends on the biomass to methane carbon conversion and battery storage capacity of CNG PHEVs. Converting biomass to methane using solar heat/H2 leads to ~65% lower LDV biomass requirement compared to standalone processes recovering ~30% biomass carbon as methane. The resulting biomass amounts compare favorably with future US biomass supply projections.